Ion implantation is a standard technique for introducing conductivity-altering impurities into a workpiece. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the workpiece. The energetic ions in the beam penetrate into the bulk of the workpiece material and are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity after activation.
Solar cells are one example of a device that uses silicon workpieces. Any reduced cost to the manufacture or production of high-performance solar cells or any efficiency improvement to high-performance solar cells would have a positive impact on the implementation of solar cells worldwide. This will enable the wider availability of this clean energy technology.
In the past, solar cells have been doped using a dopant-containing glass or a paste that is heated to diffuse dopants into the solar cell. This does not allow precise doping of the various regions of the solar cell and, if voids, air bubbles, or contaminants are present, non-uniform doping may occur. Solar cells could benefit from ion implantation because ion implantation allows precise doping of the solar cell. Solar cells, however, may require that certain patterns of dopants be implanted or that only certain regions be implanted with ions. Previously, implantation of only certain regions of a workpiece has been accomplished using photoresist. Use of photoresist, however, would add an extra cost to solar cell production because extra process steps are involved. This also poses a difficulty if the regions to be implanted are extremely small. Other hard masks on the solar cell surface likewise are expensive and require extra steps. Accordingly, there is a need in the art for an improved implant mask and, more particularly, an improved implant mask for solar cells.